1. Field of the Invention
The present invention relates to an improvement to a call control method and circuit in an electronic private branch exchange having an LCR (Least Cost Routing) function for further improving a reduction effect of the communication cost and enabling access to a particular common carrier in preference to the selection of the least cost route.
2. Description of the Related Art
Recently, going with the market release of the communication enterprises, the number of line suppliers called common carriers has been increasing.
The common carriers are line suppliers who compete in communication costs and set different charging system for use of the lines for users.
Thus, the users are free from being forced to pay a uniform expensive charge, for example, when making a call. The user can select a cheaper common carrier line to save the telephone charge.
Under the background of such situation, various service functions for efficiently accessing lines supplied by a plurality of common carriers are also added to electronic private branch exchanges. One of the service functions of this type known is the Least Cost Routing (LCR) function which automatically selects the minimum cost line from the plurality of common carriers and originates a call on the basis of dialed telephone numbers.
More specifically, in the LCR function, the minimum cost route (the minimum cost common carrier) of the lines accommodated in an electronic private branch exchange is automatically selected on the basis of dialed numbers indicative of an area code. Information required for accessing the selected common carrier is added, and then a call origination is made.
Since the exchange has such function, a user does not need to know information such as a special code "00XX" for accessing a common carrier, and is only required to dial the telephone number of a party to communicate with followed by an LCR access code to realize communication at the minimum cost.
It goes without saying that, if the communication cost involved in the use of the LCR function is considered, the communication cost is further reduced as the number of competing common carriers becomes larger and the respective differences in the communication cost become greater.
However, since the number of common carriers is small, there is no technical intention of causing a plurality of common carriers to compete positively in the present state of the LCR function. There is naturally a limit to the reduction of the communication cost.
If the LCR function operation is considered in the situation in which there are a plurality of common carriers, the respective communication costs of the common carriers vary depending on time when communication is made with the same called party. For example, the communication cost through the use of a first common carrier is minimum at a time A, while the communication cost through the use of a second common carrier is minimum at a time B, and so on.
In a conventional electronic private branch exchange, the respective priorities of the communication costs of the common carriers are fixed through all the time of use, and the selection of minimum cost route is performed on the basis of the fixed setting irrespective of time.
Thus, there may be a case where the user is forced to use an expensive route depending on a communication time, which is a hindrance to reduction of the communication cost.
The convenience of the LCR function in an electronic private branch exchange of this type is also a hindrance to access to a particular common carrier.
For example, if a user wishes to call an operator of a particular common carrier, it is impossible access to that particular target common carrier by using the LCR access code.
Therefore, if the user has a strong intention to access this particular common carrier for the reason mentioned above, the user has to find another way which does not rely on the LCR function.
One of the accessing methods employed in that case is to make a call origination using an access code or a trunk access code to directly capture a trunk corresponding to a particular desired common carrier.
When a call origination is made using this method, it is necessary to input the trunk access code instead of the LCR access code, of course.
If there are a plurality of trunk groups, it is necessary to memorize a plurality of trunk access codes individually in addition to the LCR access code and to input them accurately, so that the calling operation is very complicated.
As described above, in the conventional electronic private branch exchange, the number of routes to be selected is limited due to the small number of common carriers and thus the reduction of the communication cost is very low.
Another reason why the communication cost cannot be reduced is that there are no processes to manage the communication cost for each unit time for each common carrier, and to select a route on the basis of that management data.
Since the minimum cost route is preferentially selected in the LCR function mode in a conventional private branch exchange of this type, it is impossible to access to a particular common carrier by using such LCR function.
Even if the trunk access code is used as one of the ways to code with this problem, the user has to memorize many trunk access codes to be used in addition to the LCR access code and to input those trunk access codes thereto, which would make the calling operation complicated.